Javadoc of AbstractLeastSquaresOptimizer.guessParametersErrors() is too vague

Details

Description

This bug report follows a recent discussion available here. It is now recognized that the values returned by guessParametersErrors() are in fact known as (asymptotic) standard errors. The javadoc should be made more explicit. Besides, the values returned by this method should be tested. The reference datasets from NIST are to be used.